Super microfilaments have been used in various applications such as artificial leathers, wiping cloths and filters. However, since special and complicated spinning methods such as island-in-sea type fiber spinning (for example, Japanese Patent Laid-Open No. Hei 7-258940) or spinning by dividual fibers (for example, Japanese Patent Laid-Open 2002-220740) have been used, for the production of highly molecular oriented super microfilaments and having high quality with the fiber diameter of 5 μm or less, they are expensive and cannot be drawn simply and conveniently by using general purpose fibers.
As a method of drawing to obtain fibers with high tensile strength and high tensile modulus, the present inventors, et al. have proposed a zone drawing method (Japanese Patent Publication No. Sho 60-24852), but further requirements are desirable for stable production of fine filaments by the zone drawing.
And, the request to produce super micro fibers in the field of fibers are extended to fibers having higher function and performance. However, it is difficult to produce at stable operation as the apparatus is more complicated and precise so that is expensive by the conventional method to obtain super micro fibers. And the manufacturing methods of the conventional super micro fibers are not match the production of high performance fibers as their production is high-mix low-volume production that it has been required the manufacturing means of high performance fibers of high quality in more simple and convenient ways. Therefore, the simple and convenient method is required also in sheath-core type super microfilaments which are the typical example of high performance fibers.
On the other hand, this invention concerns drawing technology of filaments by infrared rays heating but the technology regarding these has been performed in many ways conventionally (for example, Japanese Patent Laid-Open 2003-166115, pamphlet of International Laid-Open No. 00/73556, Akihiro Suzuki, et al. “Journal of Applied Polymer Science”, Vol. 83, 1711-1716, 2002, Akihiro Suzuki and one other, Preliminary Abstracts of Polymer Science Society, Japan, May 7, 2001, Vol. 50, No. 4, pp. 787, Akihiro Suzuki and one other, “Journal of Applied Polymer Science”, Vol. 88, pp. 3279-3283, 2003, Akihiro Suzuki and one other, “Journal of Applied Polymer Science”, Vol. 90, pp. 1955-1958, 2003). Improving these technologies further, this invention is made effectively applicable to the sheath-core type filaments.